Fuses



Sept. 1, 1959 J. E. WAY 2,902,568

FUSES Filed Aug. 1, 1958 FIG. 41*

JAMES E.- WAY INVENTOR.

B fwwm United States Patent @fiice Patented Sept. 1, 1959 FUSES 3 James Way, Binghamton, N.Y. Application August 1, 1958, Serial No. 752,508

Claims." (Cl'.'200130) screwthreaded shell surrounding thebase of the fuse and by a conductive terminal boss'centered on the inner end of the fuse.

Many fuses are, installed in locations such that the fuses become subject tovibration; and/ or extreme temperature change. Even though-a prior art plug fuse may be installed by screwing it in quite tightly, -I have found that vibration and/or radical temperature change may cause the fuse tobecome loose. In order tomake good electrical contact, .the screw-threaded shells of plug fuses andthecooperatingthreaded shells of fuse receptacles commonly are made of fairly resilient copper. Economy and ease of installation and removal dictate that coarse pitch threads be used on both fuses and receptacles, and

further, that both the matingscrew parts be made sufliciently resilient sothat a certain laxity in thread tolerance will not=critical1yatfect electrical contact area. To insure proper wiping electrical contact,- the cooperating threaded portions of fuse shells. andv receptacles usually are made of soft copper, and the tip end of the fuse made of softcopper or brass. Due to manufacturing tolerances which necessarily accompany low cost devices of this nature, various fuses made by.various manufacturers, and various fuses made by a singlemanufacturer must be screweddifferent distances or a different number of turns intoa given receptacle or socket in order to make proper electrical contact.

Sometimes a given plug fuse will not make contact in a given socket until screwed in i so far that a-permanent-deformation of the socket and its threads results Thereafter, other fuses may fit poorly in such a socket, apparently making-proper electrical contact when installed, but being loosely retained due to insuflicient friction betweenthe fuse screw shell and the internally threaded socket or receptacle.

Copper of thetype commonly used in plug fuses has a considerable temperature coeflicient of expansion, so that ambient temperature changesmay cause a plug fuse which initially was installed snugly to become loose. While corresponding expansion and contraction of the involved fuse receptaclernay compensate in part for fuse shell expansion and contraction, their coefficients of expansion' often" differ, so that the fuse may become loose.

. Furthermore, plug fuses commonly are provided with a transparent window. to allow visual inspection of fuse links. Perhaps due to the delicate appearance of ordinary fuse links, or perhaps due to a fear of shock or a mistaken notion of the ruggedness of uses, many laymen improperly install fuses, neglecting to tighten them sufficiently when installing them into sockets.

A measurable resistance is involved in .any plug fuse installation, and if the fuse is loosened, due to either vibration or temperature change or both, the contact resistance may increase considerably. If a substantial amount of current is flowing through aloosenedfuse installation, the fuse and fuse socket may reach a very high temperature before the fuse blows, creating a considerable hazard. Also, and particularly in circuits subject to vibration, arcing mayioccuriwithin the fuse socket, usually severly pitting and often destroynig the fuse, the receptacle, or both.

Thus it will be seen fromthe above that an improved plug fuse which resists loosening due to vibration and/ or temperature change has been needed. The instant invention thoroughly avoids the abovementioned defects and limitations ofthe prior art in economical and practical manner.

It is therefore a primary'object of the inventionto provide an improved'plug fuse which is markedly less subject to vibration. It is a further object of the invention to provide an improved plug fuse which is less subject to temperature changes.

It is another object of the invention toiprovide an improved fuse of the abovementioned type which has a minimum number of moving parts,ieach of which is simple, reliable and economical.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in--connectionwith the accompanying drawings, in which:

Fig. 1 is a cross-section view of anassembled exemplary plug fuse constructed in accordance'with the invention;

Fig. 2 is an elevation-view of an assembled-exemplary plug fuse constructed in accordance with the invention;

Fig. 3' is an assembly view in exploded form, showing the parts of the exemplaryplugfuse of :Figs. land 2;

. and

Figs. 4a and 4b show alternative spring meanswhich may be used in constructing the invention.

Referring now to Figs. 1-3,"the exemplary plug fuse may be seen to comprise -aporcelain,--gl ass,.- ceramic or other insulatingbase 10 provided with aknurled upper periphery 11 and: a threaded base portion 12, afportion of base 10 being shown cut awayin Figs. :1 and 3 to illustrate an exemplary cross-section. Base 10 may be provided with a mica, Lucite or'other plastic transparent window as at 9 to allow the internal condition of the fuse link to be visuallydetermined. A fiber, paper or other insulating sleeve such as shown at 15 'may be provided to fit inside base 10 as best shown in Fig. 1 serving to mechanically insulate a fuse link disposedtherein: from the inner wall of base 10. Base 10 may be provided, with an internal ear or key 16 which protrudes axiallyand cooperates with slot 17 in constraining .disk 1-8,-thereby preventing axial rotation of disc 18 with respect -tobase 10. Disc 18, which is preferably plastic or ceramic, may be provided at its center with a square, hexagonal or any other non-circular shaped hole 19 which receives a correspondingly shaped end 20 of brass plunger 21. Insulating disc 18 serves a dual purpose, bothsupporting the inner end of reciprocable plunger 21 andmaintaining it in axial alignment within the cylindrical .base member, and further, providing an arc-confining seal to confine the flash accompanying fuse-link destruction to the-inner chamber of base member 10. It is quite disadvantageous in the interests of safety that fusion of the fuse link occur within a confined chamber isolated from either one or the other of the fuse external contact means. It will become apparent that disc 18 completely isolates fuse link 24 from outer shell 28 in the present invention. Square section 2t) of plunger 21 passes through an oversize hole 22 in a spring meansshown as comprising steel spring washer 23, which is preferably made of spring steel. Section 20 fits snugly in hole 19 of lock disc 18, thereby fixedly constraining plunger 21 against axial rotation with respect to base 10, or otherwise stated, insuring equal rotation of plunger 21 as base is rotated to screw the assembled fuse into or out of a receptacle. Tip 20 of a plunger 21 is electrically connected to one end of fuse link wire 24 after having been passed through holes 19 and 22, and a deformable slot 25 may be provided at tip 280 for crimping to clamp one end of fuse wire 24.

The fuse link, which may comprise either conventional circular fuse wire or fuse strap, may be disposed as shown in Fig. 1, with its other end looped through slot 26 in base 10 and doubled back as shown at 27 in Fig. 1. A groove such as shown at 28 in Fig. 2 may be provided to accommodate the end of link 24. Insulating shell 15 is preferably provided with means for supporting the mid-portion of link 24 and for maintaining such portion near window 9. As shown in Fig. 3 shell 15 may be provided with a fibre or paper band 15a around which link 24 may be looped. The critical cross-section, or most narrow portion of link 24 preferably is looped around band 15a, so that fuse destruction due to an overcurrent condition will be readily detectable through window 9.

The end of link 24 passed through slot 26 of base 10 and doubled back lies in groove 28a (Fig. 2) and slightly protrudes therefrom, so that copper or brass shell 28 wipes against and firmly compresses the doubled back end of link 24, insuring good electrical contact between shell 28 and link 24. As a further means of insuring good contact, link 24 may be soldered to shell 28, preferably near slot 26.

Spring means 23, shown as comprising a bent or deformed circular spring-steel washer fits on section 20 of plunger 21, urging disc 18 and plunger 21 apart in a manner to be more fully described below. Plunger 20 may be provided with an enlarged portion or collar 22, which serves to limit the position of spring 23. Circular portion 30 of plunger 21 passes through bore 31 of ceramic or plastic insulating dome 32, face 33 of collar 22 seating against face 34 of dome 32. Tip end 36 of plunger 21 protrudes through bore 31 of dome 32 to make contact with the center terminal of the receptacle into which the fuse is inserted. Copper or brass shell 28 is threaded to mate with the threads on portion 12 of base 10, and after shell 28 has been screwed upon that threaded portion to such an extent that narrowed neck 29 of shell 28 urges insulating dome securely against edge 13 of base 10, rim 38 of shell 28 may be crimped to grasp slot 14 in base 10, permanently aifixing shell 28 to base 10. Thus insulating dome 32 will be held in fixed axial position with respect to base 10.

When the plug fuse has been assembled, spring means 23 urges disc 18 and plunger 21 apart, and since disc 18 is seated against base 10, plunger 21 protrudes to such an extent that face 33 of collar 37 seats against face 34 of dome 32. However, as the assembled fuse is installed in a receptacle, plunger 21 is urged leftwardly with respect to dome 32 and shell 28 as viewed in Fig. 3 against the force of spring 22, compressing spring 22, and applying a spring force between plunger 21 and shell 28 commensurate with the amount that spring 23 has been deflected. This spring force may, by appropriate selection of the spring constant of spring 23, be made sufficient to prevent any appreciable loosening of the fuse regardless of vibration or radical temperature change. If desired, spring means 23 may comprise not a single crimped washer as shown but a plurality of leaf spring means of the type shown. As the assembled fuse is inserted into a receptacle, friction between tip 36 of plunger 21 and the central terminal of the receptacle will tend to rotate plunger 21 with respect to base 10. However, ear 16 and slot 17 prevent relative rotation of disc 18 with respect to base 1t), and use of a non-circular opening 19 in disc 18 and a cooperating shaped shank 20 on plunger 21 prevent relative rotation of plunger 21 with respect to disc 18, thereby preventing any rotation of the plunger 21 and of fuse link 24 that would disturb the fuse link electrical connection. As will be apparent at this point, the spring means utilized in the present invention must have considerable force, when compressed, and I chose to utilize springs having a spring constant of the order of eighty pounds per inch or more, so that an inward displacement of plunger 21 of one-eighth inch will apply about ten pounds force between the receptacle and the plug fuse. Flat springs having a single turn, of the general type shown, are greatly preferred to coil springs having plural turns in order that the axial movement of plunger 21 may be kept small while still obtaining a considerable spring force.

One important feature of the present invention is the fact that no electrical current need pass through the spring means utilized to spring load plunger 30. In order to provide sufiicient spring loading Without an awkward and bulky spring it is desirable to use spring material having a high spring constant and low fatigue, such as spring steel. With the exception of certain relatively expensive mate rials, such as beryllium copper, most materials having the requisite spring constant and low fatigue are inferior conductors, so that heating attending their usage is likely to render them disadvantageous. Inasmuch as electrical current does not pass through spring 23, this spring may comprise any desired type of spring metal selected entirely with regard to its mechanical characteristics and entirely without regard to its electrical conductivity.

A further feature of the present invention is the fact that spring means 23 may comprise a flat or leaf-type spring rather than a coil spring. Coil springs may be substituted but they have the disadvantage that in general they require more axial length for a given spring force, and greater travel of plunger 21 relative to base 10 to develop the same spring force. It is highly desirable to minimize relative displacement between the opposite fixed ends of the fuse link during installation and removal of the fuse, in order to avoid disturbing the fuse link. Use of a flat spring of the nature shown at 23 is made possible by the arrangement of the elements of the invention in such manner that no current need pass through the spring means. Fig. 4a illustrates an alternative spring means 23 formed of spring steel strap. Fig. 4b illustrates one manner in which plural springs may be mounted to urge the plunger outwardly. In Fig. 4b two springs 23b of the nature shown in Fig. 4a are disposed back-to-back on non-circular shank 20.

Certain modifications which may be made in carrying out the invention will become apparent in light of this disclosure. For example, the car 16 and slot 17 on base 10 and disc 18 may be interchanged, providing a slot in base 10 and an ear on disc 18 in lieu of the arrangement shown. Also, the invention may be applied to a number of renewable-type plug fuses known in the prior art.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efliciently attained, and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having described my invention what I desire to claim and to seure by Letters Patent is:

1. In a plug fuse, a threaded insulating base member of generally cylindrical shape having an open end, an insulating disc mounted on said open end and having a central aperture, a conductive plunger axially disposed with respect to said base member and passing through said aperture, an insulating means and a threaded conductive shell, said insulating means surrounding said plunger and insulating said plunger from said shell, said threaded shell being screwed on said threaded base memher to retain said insulating means at a fixed axial position with respect to said insulating disc, leaf compression spring means mounted between said insulating disc and said plunger, and a fuse link within said cylindrical base member connected between said plunger and said shell.

2. In a plug fuse, an insulating base member of generally cylindrical shape having a transparent window in one end and an open second end, an insulating disc having a non-circular central aperture mounted on said second end, a conductive plunger having a cooperating non-circular inner end adapted to protrude through said aperture into said base member, said insulating disc being keyed to said base member to prevent relative rotation between said disc and said base member, said plunger having a collar portion and an outer end, leaf spring means disposed on said plunger, and adapted to urge said plunger away from said insulating disc, an insulating dome member having an axial bore adapted to receive said outer end of said plunger, a hollow conductive shell having external threads to engage a receptacle, said shell serving to axially fix said insulating dome and said insulating disc with respect to said base member, and a fuse link connected between said plunger and said shell.

3. In a plug fuse, a cylindrical hollow insulating base member having an external threaded portion and one open end, a hollow conductive shell threaded internally and externally and adapted to be screwed on said base member at said open end, an insulating disc having a central aperture, a conductive plunger, an insulating means; said disc, plunger and insulating means being mounted on said open end of said base member and held on said base member by said shell, said plunger extending through said aperture into said base member and extending through said insulating means and said shell to provide an axially-located external contact terminal, spring means disposed to urge said plunger outwardly from said base member, and a fuse link within said base member connected between said plunger and said conductive shell.

4. In a plug fuse, a generally cylindrical insulating hollow base member having one open end, a generally cylindrical hollow conductive shell having external threads adapted to be screwed into a receptacle, said shell being fixedly attached to said base member at said open end, a reciprocable conductive plunger axially extending within said base member and through said shell, spring means adapted to urge said plunger outwardly from said base member, and a fuse link within said base member connected between said plunger and said conductive shell.

5. A plug fuse according to claim 4 having an insulating disc located at said open end of said base member, said disc having an aperture through which said plunger protrudes into said base member.

6. A plug fuse according to claim 4 having insulating means disposed between said plunger and said conductive shell, said insulating means having an axial bore through which said plunger protrudes, said plunger having sufficient length to extend through said insulating means and said insulating means and said conductive shell to provide an axial external terminal.

7. Apparatus according to claim 5 in which said spring means comprises a deformed flat washer compression spring disposed between said insulating disc and said plunger.

8. A plug fuse according to claim 5 in which said insulating disc is keyed to said base member to prevent relative rotation, and in which said aperture and the portion of said plunger protruding through said aperture are of non-circular cross-section to prevent rotation between said disc and said plunger.

9. Apparatus according to claim 6 in which said plunger is provided with an enlarged portion of greater diameter than said axial bore of said insulating means, whereby said insulating means limits the outward expulsion of said plunger resulting from the force of said spring.

10. In a plug fuse, a generally cylindrical insulating hollow base member having one open end, a generally cylindrical hollow conductive shell having external threads adapted to be screwed into a receptacle, said shell being fixedly attached to said base member at said open end, a reciprocable conductive plunger axially extending within said base member and through said shell to provide an axial external terminal, a fuse link within said base member connected between said plunger and said conductive shell, and a spring-steel compression spring washer disposed to urge said plunger outwardly from said base member when said spring is compressed, said terminal end of said plunger normally extending from said shell so that insertion of said shell into a receptacle compresses said spring washer, substantially increasing the mechanical threading friction between said plug fuse and said receptacle.

References Cited in the file of this patent UNITED STATES PATENTS 1,322,079 Zarlinga et a1. Nov. 18, 1919 1,681,847 Fabrey Aug. 21, 1928 2,106,109 Prendergast Jan. 18, 1938 2,108,106 Dalcher Feb. 15, 1938 2,171,866 Rowe Sept. 5, 1939 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,902,568 September 1, 1959 James Eo Way It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line '71, for "uses" read fuses 5 column 2, line 12,

for "destroynig" read me destroying line '70 for "disadvantageous" read advantageous Signed and sealed this 12th day of April 1960 Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Ofl'icer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 2,902,568 September 1, 1959 James E0 Way It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and t Patent should read as correct hat the said Letters ed below.

Column 1,. line '71, for "uses" read fuses column 2, line 12, for "destroynig" read destroying line 70, for "disadvantageous" read advantageous Signed and sealed this 12th day of April 1969 Attest:

KARL H0 AXLINE ROBERT C. WATSON Attesting Ofi'icer Commissioner of Patents 

